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When you look at the motherboard inside your computer, you notice that there are
a number of different items connected to this board. The memory sockets are
installed on this board; the CPU socket is located on the motherboard, and the BIOS
chip is also located on the motherboard. In this section, we will identify the different
system board components.
Processor
One of the easiest items to recognize on the motherboard is the processor. The processor
is usually the largest chip on the system board and can be identified generally
because it often has a heat sink or fan located on top of it.
Classic Pentium motherboards typically have a socket 7 slot that the processor is
inserted into. This socket is implemented as a ZIF (zero insertion force) socket,
which means that the processor chip can be removed or added to the socket with
very little effort. ZIF sockets typically have a lever that you
pull to pop the processor out of the socket.
Pentium II system boards had to implement a different socket for the Pentium II
chip because the Pentium II chip was designed with a single edge connector and
was inserted into the board standing up. The processor socket for Pentium II chips
is called slot 1.
SIMM/DIMM sockets
When you look at a system board, one of the first items that should stand out is the
processor or its socket; the next thing that you will usually take notice of are the
memory slots that are used to install RAM.
There are typically two types of sockets to install memory: SIMM (Single InLine
Memory Module) sockets and DIMM (Dual Inline Memory Module) sockets. Original
Pentium systems typically have either four 72-pin SIMM sockets, or two 168-pin
DIMM sockets to install memory.
When installing SIMMs in Pentium motherboards, you have to install them in pairs,
but when installing DIMMs, you can install them individually. The reason for the difference
in the installation process is that when installing memory, you must fill a
memory bank, which is the size of the processor’s data path. That is, if you install
72-pin (32-bit) SIMMs onto a Pentium (64-bit) motherboard, then you have to install
two modules to fill the 64-bit data path of the processor. DIMMs are 64-bit memory
modules, which is why you only have to install one at a time.
Cache memory
Cache memory increases performance by storing
frequently used program code or data. Because cache memory is faster than RAM,
the system can store information accessed from RAM in cache memory when the
data is accessed the first time. The processor can then retrieve the information
from the faster cache memory for subsequent calls.
All the processors today have integrated cache memory, which is known as level-1
cache. The types of cache are as follows:
L1 (level-1) cache: Cache that is integrated within the processor.
L2 (level-2) cache: Cache that is located outside the processor, like on the
motherboard.
Older motherboards implemented cache memory as rows of DIP chips placed
directly on the motherboard. This area was sometimes even labeled “cache.” Labels
on a motherboard seem to be something that you cannot always rely on though—if
they are there, consider it an added bonus!
Newer systems have implemented the cache as a memory module, so you may see
an empty slot on the motherboard that looks like a place where you would install a
SIMM, but it will really hold a cache module. A lot of times this will be labeled as
cache on the system board.
Expansion slot
Most motherboards have one or more expansion slots, which serve the purpose of
adding functionality to the computer. Even if, for example, your computer doesn’t
have sound capability right now, you can install a sound card into the expansion
slot to add that capability.
Expansion slots come in different varieties on systems today, and it is extremely
important to understand the benefits of each type.
If you look at the system board, you can see a number of expansion slots. There are
probably some white narrow slots on the board, which are the PCI slots. You may
also see some larger black slots; these are ISA slots.
Communication ports
Newer system boards have communication ports integrated directly into the board.
The communication ports are also known as the COM ports. Typically, there are
two COM ports on each system, COM1 and COM2.
COM ports are also known as serial ports. The reason that they are called serial
ports is because they send data in a series—a single bit at a time. If eight bits of
data are being delivered to a device connected to the COM ports, then the system
is sending the eight bits of data, one at a time.
You usually connect an external modem, or a serial mouse, to these ports. Each of
these devices is used for communication; a modem is used to allow your computer
to talk to another computer across phone lines, while a serial mouse is a communication
device that allows you to communicate with the system.
Serial ports on the back of the system board are one of two types:
DB9-male is a male serial port with 9 pins.
DB25-male is a male serial port with 25 pins.
Parallel port
Another type of connector that you will have on the back of the motherboard is the
parallel port. The parallel port is also known as the printer port, or LPT1. The parallel
port gets its name by being able to send information eight bits at a time.
Whereas serial ports only send one bit at a time in single file, parallel ports send
can send eight bits in one operation—side-by-side rather than single file.
The parallel port is a female port located on the back of the system board with 25
pins, which is known as DB25-female.
You connect the parallel port to a printer by using a parallel cable that has a different
type of connector at each end. On one end of the cable is a DB25 connector that
attaches to the parallel port on the back of the computer (that makes sense—a
female DB25 port has a cable with a DB25 male connector on it). On the other end
of the cable (the end that connects to the printer) you will have a 36-pin Centronics
connector.
Keyboard/mouse connector
Most motherboards today have mouse and keyboard connectors that are most
likely PS2 style connectors.
Older motherboards may have an older DIN keyboard connector, which you can see
on baby AT motherboards. These systems may or may not have a mouse port on
the system board. If not, the mouse connector was located on the case that the system
board was inserted into; the mouse connector would connect by wires to the
system board.
Power connector
Located on the system board, you should see a type of connector that you can use to
connect the power supply to the motherboard. All of these devices connected to the
motherboard need to get power from somewhere, so the power supply is connected
to the motherboard, which supplies power to the board and its components.
There are power cables coming from the power supply to connect to the motherboard with very
unique connectors on the end, these may be labeled as P1 and P2, or on some systems,
P8 and P9.
You have to be extremely careful to make sure that these connectors are inserted
properly, or you could damage the motherboard. Often, the connectors are keyed
(meaning that they can only go in one way) so that you cannot put both of the connectors
in the wrong way.
Video adapter
Many motherboards today come with a built-in video adapter, sometimes called a
video card or video controller.
Hard disk controller
A controller is a device that is responsible for controlling data flow, so a hard drive
controller is responsible for both of the following:
1. Receiving information from the processor and converting or interpreting the
information into signals that the hard disk can understand
2. Sending information back to the processor and converting the information
into signals that the processor can understand.
Older drives implemented the controller as an expansion card installed into the
system that connected to the hard disk via a cable connection. Today, however,
hard disk controllers are integrated into the hard disks.
You can also find either one or two hard disk controllers on newer motherboards
(for more information, see the section titled “EIDE/ATA-2”). The controller on the
motherboard has 40 pins and connects to the drive using a 40-wire ribbon cable.
IDE/ATA
A number of hard drive standards have been developed over the last number of
years—the first major standard being the IDE standard. The IDE (Integrated Drive
Electronics) standard calls for an integrated controller on the drive to manage information
entering and leaving the hard disk.
IDE has been around since 1989. IDE drives attach to the motherboard by means of
a 40-wire ribbon cable. The IDE standard also allows two drives to connect in a
daisy-chain fashion, creating a master/slave relationship between devices. The master
drive is responsible for sending and receiving information in the chain.
The IDE standard is also known as the ATA (Advanced Technology Attachment)
standard, which is sometimes known as the ATA-1 standard.
EIDE/ATA-2
The EIDE (Enhanced IDE) standard followed shortly after the IDE standard. The
EIDE standard is a specification that allows four drives to be connected to a dualchannel
controller. This is usually implemented as a motherboard having two controllers,
one being the primary controller and the other being the secondary
controller. You would then connect two drives off of each controller, making a master/
slave chain off each controller; EIDE also supports larger hard disks; the
typical size of an IDE drive was about 504 MB. The EIDE standard is also known as
ATA-2.
ATAPI
Typically, IDE devices are implemented as hard drives, but there has been a new
ATA specification that has allowed other types of devices to exist on an ATA (or
IDE) chain. This specification is known as the ATA Packet Interface, which allows
devices like CD-ROMs and tape drives to exist on an ATA chain. Other types of
ATAPI devices are CD writers, DVD devices, and zip drives.
ULTRA DMA
Ultra DMA drives have two major benefits over ATA drives:
Speed: Ultra DMA devices function at double the speed of regular IDE devices.
IDE devices execute commands at 16.6MB per second, whereas ultra DMA
devices execute commands at 33.3MB per second.
Reliability: Ultra DMA devices implement error correction, which provides for
increased data reliability compared with IDE, which does not implement error
correction.
To take advantage of ultra DMA technology, you need an ultra DMA drive and an
ultra DMA compatible BIOS. In addition, you need an ultra DMA compatible driver
loaded in the operating system that uses the device.
It is important to note that ultra DMA technology is backward compatible with IDE
and EIDE. For example, if you have a motherboard with ultra DMA support, you can
still plug an IDE or EIDE device into the controllers on the motherboard. You can
also take a ultra DMA drive and install it on an EIDE board.
Floppy disk controller
Located very close to the hard disk controllers, you should see a smaller floppy
drive controller that connects the floppy drive to the motherboard. This controller
supports a 33-wire ribbon cable, which connects the floppy drive to the motherboard.
When connecting the floppy drive to the system, you will notice that the ribbon
cable for the floppy drive has one end where the wires are twisted. This is the end
of the ribbon cable that must be connected to the floppy drive. The opposite end is
connected to the controller on the motherboard.
SCSI controller
Some high-end machines, particularly those designed for use as servers, may have
a controller on the motherboard with 50 pins on it. This is the footprint of a SCSI
(Small Computer System Interface) controller on the motherboard. Because SCSI
devices outperform IDE devices, SCSI controllers are extremely popular for use in
servers (which have greater hard-disk access and storage needs than regular desktop
computers).
The following list compares the various flavors of SCSI. Know them for the exam:
SCSI: SCSI is an example of a technology that has been out for many years and
has progressed within those years. The original version of SCSI, also known as
SCSI-1 was an 8-bit technology with a transfer rate of 5 Mbps. One of the major
benefits of SCSI is that you are not limited to two devices in a chain like you
are with IDE SCSI-1 allows you to have eight devices in the chain, with the controller
counting as one.
Fast SCSI-2: Fast SCSI-2 increases the performance of SCSI by doubling the
transfer rate. Fast SCSI-2 devices transfer information at 10 Mbps, as opposed
to 5 MBPS (SCSI-1). Fast SCSI-2 is still an 8-bit technology and supports eight
devices in the chain.
Wide SCSI-2: Wide SCSI-2 takes the data path of SCSI (8-bit) and doubles it to
16 bits; because the width of Wide SCSI-2 has been doubled the transfer rate is
also 10 Mbps. The number of devices in a Wide SCSI-2 chain is 16.
Fast Wide SCSI-2: Fast Wide SCSI-2 is the combination of Fast SCSI-2 and Wide
SCSI-2. The data path of Fast Wide SCSI-2 is 16 bits, the transfer rate is 20
Mbps, and the number of devices that is supported in the chain is 16.
Ultra SCSI: Ultra SCSI takes the transfer rate of 10 Mbps and doubles it again
to 20 Mbps! With Ultra SCSI, the bus width is only eight bits, and the number
of devices that exist in the chain is eight.
Ultra Wide SCSI: Ultra Wide SCSI is Ultra SCSI with the bus width increased to
16 bits and the number of devices in the chain is increased to 16! The transfer
rate of Ultra Wide SCSI has been increased to 40 Mbps.
LVD (Ultra2): Low Voltage Differential, also known as Ultra2 SCSI, has a bus
width of 16 bits and supports up to 16 devices. LVD gets its reputation from
having a transfer rate of 80 Mbps.
BIOS chip
Locating the BIOS chip on the system board is easy; it is usually rectangular in
shape and generally features the manufacturer’s name as a label on the chip. Some
of the popular manufacturers are AMI, AWARD, and IBM.
The Basic Input Output System (BIOS) is the low-level program code that allows all
the system devices to communicate with one another. This low-level program code
is stored in the BIOS chip on the motherboard.
The BIOS chip is a ROM (read only memory) chip, which means that you can read
information from the chip, but you cannot write to the chip under normal circumstances.
Today’s implementation of BIOS chips is EEPROM (Electrically Erasable
Programmable ROM), which means that you can get special software from the manufacturer
of the BIOS to write to the chip.
Why would you want to erase the BIOS? Suppose, for example, that your BIOS is
programmed to support a hard disk up to 2GB in size, but that you want to install a
new, larger hard disk instead. What can you do about it? You can contact the BIOS
manufacturer and get an update for your BIOS chip, which is usually a software program
today (in the past, you generally had to install a new chip). Running the software
program writes new instructions to the BIOS to make it aware that there are
hard disks bigger than 2GB and provides instructions for dealing with them. But
before new instructions can be written, the old instructions need to be erased.
The BIOS chip also contains code that controls the boot process for your system. It
contains code that will perform a power on self test (POST), which means that the
computer goes through a number of tests, checking itself out and making sure that
it is okay. Once it has made it past the POST, the BIOS then locates a bootable partition
and calls on the master boot record, which will load an operating system.
Battery
The computer keeps track of its inventory in what is known as Complementary
Metal Oxide Semiconductor (CMOS). CMOS is a listing of system components, such
as the size of the hard disk that is installed in the computer, the amount of RAM,
and the resources (IRQs and IO addresses) used by the serial and parallel ports.
This inventory list is stored in what is known as CMOS RAM, which is a bit of a
problem because RAM loses its content when the power is shut off. You don’t want
the computer to forget that it has a hard disk or forget how much RAM it has
installed. To prevent this sort of problem, a small watch-like battery on the system
board maintains enough energy so that CMOS RAM does not lose its charge. If
CMOS RAM loses its charge, it results in the CMOS content being lost.
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